<template>
  <transition :name="transitionName">
    <div v-show="visible" :style="customStyle" class="back-to-ceiling" @click="backToTop">
      <svg width="16" height="16" viewBox="0 0 17 17" xmlns="http://www.w3.org/2000/svg" class="Icon Icon--backToTopArrow" aria-hidden="true" style="height:16px;width:16px"><path d="M12.036 15.59a1 1 0 0 1-.997.995H5.032a.996.996 0 0 1-.997-.996V8.584H1.03c-1.1 0-1.36-.633-.578-1.416L7.33.29a1.003 1.003 0 0 1 1.412 0l6.878 6.88c.782.78.523 1.415-.58 1.415h-3.004v7.004z" /></svg>
    </div>
  </transition>
</template>

<script>
  export default {
    name: 'BackToTop',
    props: {
      visibilityHeight: {
        type: Number,
        default: 400
      },
      backPosition: {
        type: Number,
        default: 0
      },
      customStyle: {
        type: Object,
        default: function() {
          return {
            right: '50px',
            bottom: '50px',
            width: '40px',
            height: '40px',
            'border-radius': '4px',
            'line-height': '45px',
            background: '#e7eaf1'
          }
        }
      },
      transitionName: {
        type: String,
        default: 'fade'
      }
    },
    data() {
      return {
        visible: false,
        interval: null,
        isMoving: false
      }
    },
    mounted() {
      window.addEventListener('scroll',  this.handleScroll)
    },
    beforeDestroy() {
      window.removeEventListener('scroll', this.handleScroll)
      if (this.interval) {
        clearInterval(this.interval)
      }
    },
    methods: {
      handleScroll(e) {
        console.log(e.target.scrollTop)
        // console.log(document.getElementById('layout').offsetTop)
        console.log(window.pageYOffset)
        // console.log(this.visibilityHeight)
        this.visible =  window.pageYOffset > this.visibilityHeight
        // this.visible =  e.target.scrollTop > this.visibilityHeight
      },
      backToTop() {
        // if (this.isMoving) return
        // const start =  document.getElementById("layout").pageYOffset
        // let i = 0
        // this.isMoving = true
        // this.interval = setInterval(() => {
        //   const next = Math.floor(this.easeInOutQuad(10 * i, start, -start, 500))
        //   if (next <= this.backPosition) {
        //     document.getElementById("layout").scrollTo(0, this.backPosition)
        //     clearInterval(this.interval)
        //     this.isMoving = false
        //   } else {
        //     document.getElementById("layout").scrollTo(0, next)
        //   }
        //   i++
        // }, 1000)
            window.scrollTo(0,0)
      },
      easeInOutQuad(t, b, c, d) {
        if ((t /= d / 2) < 1) return c / 2 * t * t + b
        return -c / 2 * (--t * (t - 2) - 1) + b
      }
    }
  }
</script>

<style scoped>
  .back-to-ceiling {
    position: fixed;
    z-index: 9;
    display: inline-block;
    text-align: center;
    cursor: pointer;
  }

  .back-to-ceiling:hover {
    background: #d5dbe7;
  }

  .fade-enter-active,
  .fade-leave-active {
    transition: opacity .5s;
  }

  .fade-enter,
  .fade-leave-to {
    opacity: 0
  }

  .back-to-ceiling .Icon {
    fill: #9aaabf;
    background: none;
  }
</style>
